Hijack - A Unique Interface to IPhone, IPad and other Audio Devices

c9afcf6bebb23ffccc5bff7b3eceb055.image.300x2251In appreciation for my help on the glass buster and other projects, my producer friend gave me a new iPad .  Very generous and appreciated.  This of course opens up a new world of applications and projects and a sudden interest in magazine articles about interfacing to the device.

In the current issue of Nuts&Volts, there is an article about using an iPxxx as a moisture meter for watering plants.  It connects using only the audio port and uses no external power source.  At a quick glance, I guessed they were using the microphone input as a ADC to measure moisture content but a longer look showed there was more to the system than that.

The moisture meter is based on a Project HiJack interface.  This is a fascinating interface developed by Ye-Sheng Kuo, Thomas Schmid and Prabal Dutta at the University of Michigan and was presented at the ISLPED’10 Design Contest.  The paper presented for the contest is very informative and can be found here.   This incredibly cheap interface has two unique features that allow it to be used with many audio devices: 1) It derives power from an audio signal to power the required circuitry and 2) it used audio tones to create a bi-directional interface over the audio path.  One of the driving goals to to create a low-cost interface that could be used with a huge range of sensors in developing countries.  One of the awesome demonstration projects is a 2-lead EKG.

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Building a Web Site - New Technology is Changing The Game

pc fix[Aurthor's Note: I wrote this article several years ago for another website.  The information is still accurate.  "Doug In The Woods" wrote to my Clever4Hire email address asking for some guidance, so this seemed like a useful reference to republish.]

Having your own web site used to be a daunting task, beyond the reach of casual users. Expensive hardware and software or costly hosting services were required to get a web site on line. Design of a web page required complicated software and an extensive knowledge of HTML to design nice looking pages.

I'm happy to report that recent technology has changed this situation so that nearly anyone can afford to have a nice looking web site! You might be surprised to learn that the total cost to have your own web page is only about $10/year! And no costly software is required to create the pages for the site.

Domain registration, hosting, page creation software? How can the web site cost only $10/year?

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EEVblog #262 – World’s Simplest Soft Latching Power Switch Circuit

Dave's got another great video on how to use a simple push-button switch as an on/off power switch.  Using this circuit can save the cost of a high-current toggle switch and makes a very clean user interface.  As usual, Dave carefully explains the details of the circuit in a clear, concise manner.

Watch the video for complete details.


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EngBlaze: How to turn your breadboard rat nest into a badass circuit – PCB manufacturing tips

From EngBlaze comes a great article on turnings a rats nest of wires into a circuit board.  The article is filled with good tips!

I've quoted four sections of the article below.  Trust me, I know how easy it is to make these mistakes! 

The Full Article

Double check RX and TX pinout

In standard electronics nomenclature, serial TX stands for “transmit” and RX stands for “receive”.  Unfortunately, part manufacturers aren’t always so kind.  On some devices, TX is an input and RX is an output, defying all logic (or using some twisted reasoning where you need to tie both “RX”s  and “TX”s together).  Even if they do use the normal notation, it’s easy to get things crossed up, so make sure you double check your prototype connections before you implement them in your PCB schematic.

Check the overall footprint of your board

Notice a theme with the checking yet?  Welcome to the wonderful life of an engineer.  As a real engineer, you’re responsible for real things, often expensive ones.  As un-glamorous as it is, double checking just about everything ensures that you only have to make that expense once, not twice.

In this case, it’s important to check the footprint of your board to make sure that your components are placed and sized correctly, and won’t get in the way of each other.  The best way to do this is to print out your silkscreen layer 1:1 on paper.  If you have chips or components that you’ll be using on the board, place them on the paper to see if their footprints are correct.

Read more: EngBlaze: How to turn your breadboard rat nest into a badass circuit – PCB manufacturing tips

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Dave has posted another excellent video blog, this one a hack he did on a Hakko FX-880 soldering iron.  The hack is interesting because he solves a design problem  and explains in detail the circuit he uses.  It's a worthwhile watch to see his methodology in problem solving.  It's good to note that his solutions don't always work out, but he analyzes the results and adapts.

Geoff's Projects: The Maximite BASIC Computer

From Geoff's Projects Blog comes the Maximite BASIC computer.  It looks like an interesting bit of kit and the table of contents at the blog has some other interesting topics.

The Maximite is a small and versatile computer running a full featured BASIC interpreter with 128K of working memory.

It will work with a standard VGA monitor and PC compatible keyboard and because the Maximite has its own built in SD memory card and BASIC language you need nothing more to start writing and running BASIC programs.

The Maximite also has also 20 input/output lines which can be independently configured as analog inputs, digital inputs or digital outputs.  You can measure voltage, frequencies, detect switch closure, etc and respond by turning on lights, closing relays, etc - all under control of your BASIC program.

The design and the firmware including the BASIC interpreter is free to download and use.   And all this is powered by a single chip which costs just US$8.44.

The Maximite was described in the March, April and May 2011 issues of Silicon Chip magazine. 

The mini Maximite was described in the November 2011 issue of Silicon Chip magazine. 

If you have not read the articles you can find out all you need to know by clicking on the links below:

Check out the rest of the article at Geoff's Projects.

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EDN: Bonnie Baker on Temperature Sensors

Part 4 of Texas Instrument's Bonnie Baker's series on temperature sensors was just publsihed.  The series starts with a comparison of sensor types and goes up to explain the details of using each type.

If you're considering what type of temperature sensor to use, or how to make an existing sensor work, Bonnie's article will be very useful.

Click the titles to open each article in a new page.  At the top of each page is a link to a pdf of each section if you'd like to print them out.


Designing with temperature sensors, part one: sensor types

Most people have heard the phrase "Birds of a feather flock together," which describes people who have similar characteristics or interests and choose to spend time together. Is it possible that some temperature sensors tend to flock together, too?

Bonnie Baker, Texas Instruments -- EDN, September 22, 2011

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Measurement Tools for Laying Out Circuit Boards and Enclosures

ruler   caliper - 300When laying out panels or circuit boards, accurate measurements are a must.  A few inexpensive tools can make excellent results much easier to achieve. 

I think we've all used rulers to try and measure parts.  For the fuse holder shown, it can be held against the ruler, the width estimated and the marks correctly interpreted to get a decent result.  The ruler shown is a high-quality metal ruler and it has metric units on the back.  I use a combination of inch and metric units depending on what size something is designed for - for example, in laying out PCB dimensions, I'll use whatever units the enclosure was designed in.  Usually, one system will provide nice numbers.

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EEVBlog #221: Lab Power Supply Design Part 1

EEVBlog 221Dave Jones at the EEVBlog has created another awesome video that's recommended viewing for all: 

EEVBlog #221:  Lab Power Supply Design Part 1.  Dave goes through all of the design considerations and calculations for a micro-controlled power supply.  He starts with the basic LM317 regulator for constant current and constant voltage and goes over the limitations.

Dave provides a great look at the design process and calculations involved.


 EEVblog #221 – Lab Power Supply Design – Part 1

 EEVblog #222 – Lab Power Supply Design – Part 2

 EEVblog #224 – Lab Power Supply Design – Part 3

EEVblog #225 – Lab Power Supply Design Part 4 – PWM Control

EEVblog #232 – Lab Power Supply Design Part 5

Note the link to the schematic on the above page.




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Andrew Carter's Blog - A Great Beginner's Resource


\Andrew Carter has a great series of blog articles covering the basics and not-so-basics of electronics components on the EEWeb site.  EEWeb is a great resource and worth checking out.

Andrew's articles so far include:

These short articles are definitely worth reviewing.  You might be surprised at what you'll learn.

Be sure to keep an eye on Andrew's posts.  I suspect many more winners are on the way.


 Updated List as of 27 December 2011

Here's a list of current blog topics.   Rather than spending an hour entering links to each section, follow the general link below.

  • Resistance, Resistors and Ohm’s Law
  • Capacitor Basics
  • Introduction to Carbon Composition Resistors
  • Overview of the Film Type Resistors
  • Get To Know the Wirewound Type Resistors
  • How to Read Resistor Color Coding Scheme
  • Capacitors in Series
  • Capacitors in Parallel
  • Resistor Values Calculation
  • Series Combination of Resistors
  • Dealing with Surface Mount Resistors
  • Learning About Resistors in Parallel
  • Know More about Voltage Divider Circuits
  • Series-Parallel Combinations of Resistors
  • A Look at the Power Rating of Resistors
  • Getting To Know the Potential Difference
  • Behavior of Resistors in AC Circuits
  • Identifying the Characteristics of Capacitors
  • Let’s Talk About Capacitance and Charge
  • Parallel Connections of Capacitors
  • Characteristics of Inductors
  • Studying the Color Codes of Capacitors
  • Getting Familiar with Capacitors
  • What’s More Inside A Capacitor
  • Capacitor Types
  • Series Connections of Capacitors
  • How Capacitors Behave in AC Circuits
  • Choosing the Type of Inductor
  • Inductance, Power and Energy of an Inductor
  • The Basics of Inductor
  • More of Self Inductance and Mutual Inductance
  • Series Connection of Inductors
  • Parallel Connection of Inductors
  • Inductive Reactance
  • RL Circuits
  • The Basics of Semiconductors
  • Describing the P-N Junction
  • Introduction to Diodes
  • Types of Diodes

Andrew Carter's Blog

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